Solids Volume Measurement in Ethanol Production


General Process Information

Grain is delivered by truck or rail to the ethanol plant where it’s loaded in storage bins designed to hold enough grain to supply the plant for 7–10 days. The grain is screened to remove debris and ground into course flour. During the cook process, the starch in the flour is physically and chemically prepared for fermentation. The milled grain is mixed with process water and an alpha-amylase enzyme is added. The slurry is heated to 180–190°F for 30–45 minutes to reduce viscosity. The slurry goes through primary and secondary liquefaction processes in order to break down the starch into short chain dextrins. Glucoamylase is added as the mixture is pumped into the fermentation tanks.

Once inside the fermentation tanks, the mixture is referred to as mash. The glucoamylase enzyme breaks down the dextrins to form simple sugars. Yeast is added to convert the sugar to ethanol and carbon dioxide. The mash is then allowed to ferment for 50–60 hours, resulting in a mixture that contains about 15% ethanol as well as the solids from the grain and added yeast. 


Co-Product Processing

During the ethanol production process, two valuable co-products are created: carbon dioxide and distillers grains. The stillage from the bottom of the distillation tanks contains solids from the grain and added yeast as well as liquid from the water added during the process. It’s sent to centrifuges for separation into thin stillage (a liquid with 5–10% solids) and wet distillers grain. It is sent through a multiple-effect evaporation system where it is concentrated into syrup containing 25–50% solids. This syrup, which is high in protein and fat content, is then mixed back in with the wet distillers grain (WDG). With the added syrup, the WDG still contains most of the nutritive value of the original feedstock plus the added yeast, so it makes an excellent cattle ration for local feedlots and dairies. After the addition of the syrup, it’s conveyed to a wet cake pad, where it is loaded for transport.

WDG must be used soon after it’s produced because it spoils easily. So, it’s often sent through a drying system to remove moisture and extend its shelf life. This dried distillers grain (DDG) is commonly used as a high-protein ingredient in cattle, swine, poultry, and fish diets.


Grain Storage

Application: Grains are delivered by trucks or rail to the plant where it is analyzed, unloaded and pre-cleaned prior to loading into storage silos designed to supply the plant for 7-10 days.

Challenges:The grains storage silos are large in size and it is essential to know the silo contents in order to closely monitor inventory levels and ensure an ongoing production process. Accurately measuring the amount of grain in the silos gives plant managers an understanding of how much grain was used in the manufacturing process of the ethanol, allowing them to better calculate the cost of goods sold and the profitability of the plant. The size of the silos makes it problematic for conventional instrumentation to yield accurate volume measurements of the stored material. Rosemount's 3D Solids Scanner system can accurately and reliably measures the volume of the stored grain, and also presents a real-time 3D profile showing how the material is distributed inside the silo.


Dried Distillers Grains

Application: WDG are often sent through a drying system to remove moisture and extend shelf life. These dried distillers grains are commonly used as high-protein ingredients in cattle, swine, poultry and fish diets. The DDGS are removed from site by conveyor to an adjacent dedicated storage silo/warehouse.

Challenges:The DDGS are stored in very large silos/warehouses/open bins. The material (containing about 10% fat and corn oil) is sticky and can settle in irregular shapes. This combination presents a real problem for end-users trying to assess the inventory levels. The Rosemount Multi-Scanner system solves this problem and can provide a highly accurate profile and volume reading in any type of silo/warehouse/open bin.

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